Hemifacial microsomia (HFM) is the second most common craniofacial malformation, yet there have been few studies of its impact on affected children. We have conducted the first large scale follow- up study of 6 to 8 year old children with HFM to evaluate psycho-social and other sequelae. We propose to continue to follow this cohort at 12 to 14 years of age after having identified that affected children had worse neuropsychological performance and higher levels of internalizing behavior problems compared to children in a demographically-matched control group. However, these findings were based on two screening instruments administered by each child's teacher. It is essential to confirm these findings with more reliable and precise assessment methods that address a wider array of neuropsychological abilities, and with more extensive measurement of potential mediators and moderators. We will evaluate neuropsychological, psychosocial, and sleep outcomes. The cohort includes 195 cases and 570 age- and geographically-matched controls from across the U.S. and Canada. In the proposed follow up study, 2 controls per case would be selected for direct, in-person assessment by trained psychometrists. Data collection would take place at the Boston and Seattle sites for nearby study subjects. The same team of psychometrists will travel for community- based assessments of study subjects that live farther away. Test batteries will cover six domains and 13 sub-domains, including academic achievement, speech and language, memory, executive function, processing speed, and perceptual motor skills. Hearing, vision, and speech impairments; sleep disordered breathing; and anesthesia exposure may be in the causal pathway between HFM and neuropsychological and psychosocial outcomes, but were not adequately measured in the study of 6 to 8 year olds. In the proposed follow-up study, standardized measurement of these important potential mediating factors on both HFM cases and controls will allow more accurate analysis of their effects. The case group includes a range of phenotypes from isolated mild facial asymmetry to severe mandibular, auricular, and orbital hypoplasia with cranial nerve paralysis and extracranial malformations, allowing subgroup analyses according to severity. Findings from our follow up study of 6-8 year olds with HFM suggest that affected children may need extra resources to achieve their highest potential. This cohort of almost 200 children affected with HFM is the only of its kind, offering the rare opportunity to continue the work that began more than ten years ago, with the goal of providing key information to families and clinicians of individuals affected with HFM.